Upon color development of an exposed silver halide photographic light-sensitive material, an oxidized aromatic primary amine developing agent reacts with a coupler to form a dye, with a dye image thus being formed. In this system, color reproduction is usually carried out using a subtractive method, and in order to reproduce blue, green and red color, yellow, magenta and cyan color images which are in a complementary relation thereto, respectively, are formed. In general, pyrazolone, cyanoacetyl or indazolone type couplers are used for the formation of magenta color images.
In one of the most preferred embodiments of color photographic light-sensitive materials, dye image-forming couplers are added to silver halide emulsions. Couplers added to emulsions must be rendered nondiffusible (or diffusion-resistant) in a binder matrix of the emulsions.
Most well-known conventional magenta color image-forming couplers are 4-equivalent couplers. However, various kinds of 2-equivalent couplers are also known, as described in various patents. Since 2-equivalent couplers require only one half the silver halide as compared with ordinary 4-equivalent couplers to form a dye, their use enables rapid processing of light-sensitive materials due to the thinness of the light-sensitive layers, and the photographic properties are improved due to a reduction in film thickness, and the economic advantages are achieved.
Various 5-pyrazolone type couplers are known for forming magenta color images. For instance, as the substituents at the 3-position of the 5-pyrazolone ring, an alkyl group, an aryl group, an alkoxy group as described in U.S. Pat. No. 2,439,098, a ureido group as described in U.S. Pat. No. 3,558,319, an anilino group as described in U.S. Pat. No. 2,311,081 (U.S. Pat. Re. No. 22,329), a dialkylamino group as described in U.S. Pat. No. 3,615,506, and an acylamino group, are known.
3-Acylamino-5-pyrazolone type couplers are frequently described, as in U.S. Pat. Nos. 2,369,489, 2,600,788, etc. However, few attempts have been known to improve this type of couplers by modifying the acylamino group.
For instance, the 3-position of the 5-pyrazolone ring can be substituted with a benzamido group, an acetamido group, a straight chain alkanamido group, a phenylacetamido group, a phenoxyacetamido group, or a naphthamido group as described in U.S. Pat. No. 2,369,489, or can be substituted with a benzamido group, an acetamido group, a phenylacetamido group or a phenoxyalkanamido group as described in U.S. Pat. No. 2,600,788. Also, the 3-position of the 5-pyrazolone ring substituted with a secondary branched alkanamido group is described in Japanese patent publication No. 16058/74.
The compounds described in these references exhibit fairly good color forming properties. However, these compounds have the disadvantage that they require a large amount of a coupler solvent which must be used for the incorporation of the couplers into an emulsion due to the poor solubility thereof in the organic solvent, and as a result it is difficult to reduce the thickness of the layer containing the couplers. Thus, improvement in the sharpness of the images formed cannot be adequately achieved, and the amount of the coupler solvent cannot be reduced, since the color forming property thereof is influenced by any change in the amount of solvent used.
The couplers according to the present invention are considerably improved couplers which have few of the disadvantage as described above with respect to the fundamental properties required for use in photographic light-sensitive materials.